This invention relates to treatment of a hydrocarbon-containing subterranean formation. In one of its aspects this invention relates to altering the permeability of a subterranean formation. In another of its aspects this invention relates to selectively plugging the more permeable portions of a hydrocarbon-containing formation. In yet another aspect of the invention it relates to enhanced oil recovery procedures utilizing the passage of a sweep fluid through an underground formation in which the more permeable portions had been selectively plugged.
It is well known in the treatment of hydrocarbon-containing underground formations that it is important to control the flow of sweep fluids through the reservoir so that the less permeable portions of the reservoir which contain the greatest part of the residual hydrocarbon can be adequately treated for removal of these hydrocarbons. The generation in a reservoir of foam which can be driven preferentially into the more permeable strata is a recognized method for effectively sealing permeable portions of a subterranean formation thereby allowing subsequent control of the flow of treating fluid in the formation. Although a wide variety of surfactants can be combined with various fluids to generate a foam in situ in a formation those skilled in the art are always interested in combination of components that can provide a foam that has characteristics that can be tailored to specific needs.
It has now been discovered that the combination of liquid or dense phase carbon dioxide with aqueous surfactant solutions produces a foam that in comparison to the commonly used combination of aqueous surfactant solution and gaseous carbon dioxide yields relatively higher resistance factors calculated from tests in which aside from the operating temperature which determines the state of the carbon dioxide the conditions were equivalent. It is, therefore, evident that the combination of liquid or dense phase carbon dioxide with an aqueous surfactant solution can produce foams eminently suited to the plugging of the more permeable portions of underground formations.
It is therefore an object of this invention to provide a method for plugging permeable portions of underground formations. It is another object of this invention to provide a method for directing flow of sweep fluid through an underground formation. It is still another object of this invention to provide a method for treating hydrocarbon-containing underground formations.
Other aspects, objects and the various advantages of this invention will become apparent upon reading this specification and the appended claims.